U.S. patent number 7,408,399 [Application Number 11/439,459] was granted by the patent office on 2008-08-05 for active driving of normally on, normally off cascoded configuration devices through asymmetrical cmos.
This patent grant is currently assigned to International Rectifier Corporation. Invention is credited to Maurizio Salato, Marco Soldano.
United States Patent |
7,408,399 |
Salato , et al. |
August 5, 2008 |
Active driving of normally on, normally off cascoded configuration
devices through asymmetrical CMOS
Abstract
Disclosed is a method of controlling a High Electron Mobility
Transistor (HEMT) through a cascode circuit, the cascode circuit
including first and second switches, a capacitor connected to a
source of the first switch, a source of the HEMT being connected to
the drain of the first switch, and a controller for controlling the
first and second switches. The method is achieved by defining state
A, where the first switch is controlled to be OFF resulting in the
HEMT being OFF and the second switch is controlled to be ON
allowing the capacitor to be charged and stabilizing the drain
voltage of the HEMT at around the HEMT gate threshold voltage. The
method further defines state B, where the first switch is
controlled to be ON resulting in the HEMT being ON and the second
switch is controlled to be OFF almost all the time, thereby
preserving the charge stored in the capacitor. Moreover, the method
provides transitioning from state A to state B to turn the HEMT ON;
and transitioning from state B to state A to turn the HEMT OFF,
wherein the first switch is switched-OFF and the second switch is
switched-ON allowing for quicker charge of the output capacitance
of the first switch from the capacitor to keep the HEMT OFF.
Inventors: |
Salato; Maurizio (El Segundo,
CA), Soldano; Marco (El Segundo, CA) |
Assignee: |
International Rectifier
Corporation (El Segundo, CA)
|
Family
ID: |
37513786 |
Appl.
No.: |
11/439,459 |
Filed: |
May 23, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060290407 A1 |
Dec 28, 2006 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
60694330 |
Jun 27, 2005 |
|
|
|
|
Current U.S.
Class: |
327/427; 326/82;
327/108; 327/429; 327/567; 327/574 |
Current CPC
Class: |
H03K
17/04123 (20130101); H03K 17/6877 (20130101); H03K
2017/6875 (20130101) |
Current International
Class: |
H03K
17/687 (20060101); H03K 19/0175 (20060101) |
Field of
Search: |
;327/427,429,108,109
;323/225 ;326/25,17,119 ;257/225,192 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tra; Quan
Assistant Examiner: O'Toole; Colleen
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is based on and claims benefit of U.S. Provisional
Application Ser. No. 60/694,330, filed on Jun. 27, 2005, entitled
ACTIVE DRIVING OF NORMALLY ON, NORMALLY OFF CASCODED CONFIGURATION
DEVICES THROUGH ASYMMETRICAL CMOS, to which a claim of priority is
hereby made and the disclosure of which is incorporated by
reference.
Claims
What is claimed is:
1. A cascode circuit having source and drain terminals for driving
a High Electron Mobility Transistor (HEMT) having first and second
source terminals and first and second gate terminals, the first
source and gate terminals of the HEMT being connected to the drain
of the cascode circuit and the second gate terminal of the HEMT
being connected to the source of the cascode circuit, the circuit
comprising: first and second switches, each having source, drain
and gate terminals, the first and second switches being connected
at their drain terminals; a capacitor connected between the source
terminals of the first and second switches; the HEMT having the
second source terminal connected to the drain terminals of the
first and second switches; and a controller for controlling the
first and second switches being connected to the gate terminals of
the first and second switches.
2. The circuit of claim 1, wherein the second switch is a P-channel
switch comprising a low voltage Metal-Oxide Semiconductor
Field-Effect Transistor (MOSFET).
3. The circuit of claim 2, wherein the first switch comprises an
N-channel switch, wherein the N-channel and P-channel switches
together form a complementary metal-oxide semiconductor (CMOS)
structure controlled by the controller.
4. The circuit of claim 3, wherein the N-channel switch carries
substantially all the current through the HEMT and the P-channel
switch directs current flow between the capacitor and the N-channel
switch.
5. The circuit of claim 3, wherein the structure operates in
accordance with states A and B and transitions from the state A to
state B and from state B to state A.
6. The circuit of claim 5, wherein in the state A the N-channel
switch is controlled to be OFF resulting in the HEMT being OFF and
the P-channel switch is controlled to be ON, which allows the
capacitor to be charged, and stabilizes the drain voltage of the P-
and N-channel switches at around the HEMT gate threshold
voltage.
7. The circuit of claim 6, wherein the P-channel switch acts as a
synchronous rectifier, allowing a lower voltage drop than a diode
and faster charging of the capacitor.
8. The circuit of claim 5, wherein in state B the N-channel switch
is controlled to be ON resulting in the HEMT being ON and the
P-channel switch is controlled to be OFF almost all the time,
thereby preserving the charge stored in the capacitor.
9. The circuit of claim 5, wherein during the transition from state
A to state B the N-channel switch is switched-ON after the
P-channel switch is switched-OFF.
10. The circuit of claim 5, wherein during the transition from
state B to state A the N-channel switch is switched-OFF and the
P-channel switch is switched-ON allowing for quicker charge of an
output capacitance of the N-channel switch from the capacitor
thereby keeping the HEMT OFF.
11. The circuit of claim 10, further comprising the effect of the
drain to source voltage V.sub.DS of the N-channel switch, wherein
before the V.sub.DS voltage reaches a HEMT threshold voltage, the
HEMT is fully ON, when the V.sub.DS voltage reaches the HEMT
threshold voltage, the HEMT starts to switch-OFF, thereby reducing
current flow in the HEMT, and the output capacitance of the
N-channel switch is charged by any residual load or leakage current
from the HEMT.
12. A method of controlling a High Electron Mobility Transistor
(HEMT) having first and second gate and source terminals through a
cascode circuit, the cascode circuit including first and second
switches each having gate, source, and drain terminals, a capacitor
connected between the source terminals of the first and second
switch, the first source terminal of the HEMT being connected to
the drain terminals of the controlling switches, and a controller
for controlling the first and second switches, the method
comprising the following steps: defining state A, where the first
switch is controlled to be OFF resulting in the HEMT being OFF and
the second switch is controlled to be ON allowing the capacitor to
be charged and stabilizing the drain voltage of the first and
second switches at around the HEMT gate threshold voltage; defining
state B, where the first switch is controlled to be ON resulting in
the HEMT being ON and the second switch is controlled to be OFF
almost all the time, thereby preserving the charge stored in the
capacitor; transitioning from state A to state B to turn the HEMT
ON; and transitioning from state B to state A to turn the HEMT OFF,
wherein the first switch is switched-OFF and the second switch is
switched-ON allowing for quicker charge of the output capacitance
of the first switch from the capacitor to keep the HEMT OFF.
13. The circuit of claim 12, wherein the first switch is a low
voltage N-channel Metal-Oxide Semiconductor Field-Effect Transistor
(MOSFET).
14. The circuit of claim 13, wherein the second switch acts as a
synchronous rectifier, allowing a lower voltage drop than a diode
and a faster supply capacitor charge.
15. The circuit of claim 13, wherein during the transition from
state A to state B the first switch is switched-ON after the second
switch is switched-OFF.
16. The circuit of claim 13, transitioning from state B to state A
comprises the effect of the drain to source voltage V.sub.DS of the
first switch, wherein before the V.sub.DS voltage reaches a HEMT
threshold voltage the HEMT is fully ON, when the V.sub.DS voltage
reaches the HEMT threshold voltage the HEMT starts to switch-OFF,
thereby reducing current flow through the HEMT, and the output
capacitance of the N-channel switch is charged by any residual load
or leakage current from the HEMT.
17. A cascode circuit for driving a High Electron Mobility
Transistor (HEMT) having first and second source terminals and
first and second gate terminals, the first source and the first
gate terminals being connected to a HEMT drain and the second gate
terminal being connected to a HEMT source, the circuit comprising:
a switching stage including high and low switches each having
source, drain, and gate terminals, the drain terminals of the high
and low switches being connected at a switching node and to the
second source terminal; a capacitor connected between the source
terminals of the high and low switches; and a controller for
controlling the switching stage, wherein the high switch is acts as
a synchronous rectifier, allowing a lower voltage drop than a diode
and faster charging of the capacitor.
18. The circuit of claim 17, wherein the low switch is N-channel
and carries substantially all the current through the HEMT and the
high switch is P-channel and directs current flow between the
capacitor and the low switch.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a cascode switching structure and,
more particularly to using a low voltage P-channel MOSFET whose
source is connected to a capacitor and its drain to a drain of a
driver switch.
A cascode circuit is a technique for improving a performance of an
analog circuit. It provides a very useful two-transistor
configuration formed of a common source stage followed by a common
gate stage. The cascode combines the two amplifier stages for
increased output resistance and reduced parasitic capacitance,
resulting in a high gain with increased bandwidth. The cascode
provides better high-frequency performance and higher output
resistance.
The cascoded configuration of a normally ON depletion mode and a
normally OFF semiconductor devices allows reliable and safe
operation in switching mode power supply systems.
Simple coupling of those two parts rely upon their own parameters
for dynamic behavior, especially during a switch-OFF. The proposed
arrangement enhances the switch-OFF transient, making use of the
charge stored in V.sub.CC supply capacitor.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid a loss of a diode
drop when a rectifier is used.
It is another object of the present invention to force a switch-OFF
transition to be faster.
Other features and advantages of the present invention will become
apparent from the following description of the invention that
refers to the accompanying drawings.
Disclosed is a method of controlling a High Electron Mobility
Transistor (HEMT) through a cascode circuit, the cascode circuit
including first and second switches, a capacitor connected to a
source of the first switch, a source of the HEMT being connected to
both the drains of the first and second switches, and a controller
for controlling the first and second switches. The method is
achieved by defining state A, where the first switch is controlled
to be OFF resulting in the HEMT being OFF and the second switch is
controlled to be ON allowing the capacitor to be charged and
stabilizing the drain voltage of the P- and N-channel switches at
around the HEMT gate threshold voltage. The method further defines
state B, where the first switch is controlled to be ON resulting in
the HEMT being ON and the second switch is controlled to be OFF
almost all the time, thereby preserving the charge stored in the
capacitor. Moreover, the method provides transitioning from state A
to state B to turn the HEMT ON; and transitioning from state B to
state A to turn the HEMT OFF, wherein the first switch is
switched-OFF and the second switch is switched-ON allowing for
quicker charge of the output capacitance of the first switch from
the capacitor to keep the HEMT OFF.
The present invention avoids loses from the diode drop by charging
a capacitance C through a channel with a resistive behavior.
Additionally, the switch-OFF transition is forced to be faster by
balancing a charge between the V.sub.CC capacitor and a cascoded
driver switch output capacitance
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a circuit utilizing the cascode circuit of
the preferred embodiment of the present invention; and
FIG. 2 is a graph illustrating the effect of state transitions of
the cascode circuit on the various voltages and a current.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
FIG. 1 illustrates a circuit 10 of the preferred embodiment of the
present invention. The circuit 10 includes a low voltage P-channel
Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) or
switch M2. The P-channel MOSFET may be obtained by doping a
semiconductor to increase the number of free positive charge
carriers. In circuit 10, the source of the P-channel switch M2 is
connected to a V.sub.CC capacitor C and the drain of the switch M2
is connected to a source S2 of a High Electron Mobility Transistor
(HEMT) 12. This transistor 12 is being driven by a driver
integrated circuit (IC) 14 through Ml cascoded transistor driver.
HEMT 12 is a depletion mode normally on device and may be based on
GaN technology. In order for it to turn off, one of the two gates
(G2 in FIG. 1, but Gl might also apply) has to be kept at the
lowest possible potential with respect to the remaining three
devices' pins and below a threshold voltage with respect to its
source pin.
The circuit 10 further illustrates a complementary metal-oxide
semiconductor (CMOS) structure formed by the P-channel switch M2
and an N-channel switch M1. The structure is controlled by the
controller IC 14. The switch M1 carries all the HEMT current, while
the switch M2 manages a current flow between the capacitor C and
Coss of the switch M1. A gate of the switch M2 is controlled so as
to maximize the advantage of the described CMOS structure.
The inventive CMOS structure operates in accordance with the
following states and transitions. In state A, the cascoded switch
M1 is controlled to be OFF, as a result, in accordance with the
cascode structure, the HEMT is kept OFF. The switch M2 is
controlled to be ON allowing the capacitor C to be charged from S2.
S2 is stabilized at around the HEMT gate threshold voltage. In
state A, the switch M2 acts as a synchronous rectifier, allowing a
lower voltage drop then a diode and a faster supply capacitor
charge.
In state B, the cascoded switch M1 is controlled to be ON resulting
in the HEMT also to be fully ON. The switch M2 is controlled to be
OFF, thereby preserving the charge stored in the V.sub.CC supply
capacitor C. In state B, the controller IC 14 manages to switch the
cascoded switch M1 almost fully ON.
When the circuit 10 transitions from state A to state B, the
cascoded switch M1 is being switched-ON while the switch M2 is
being switched-OFF. In accordance with CMOS structure of the
present invention, the switch M2 switches-OFF before the cascoded
switch M1 switches-ON. This is shown by the dead-time in FIG.
2.
When the circuit 10 transitions from state B to state A, the
cascoded switch M1 is being switched-OFF while the switch M2 is
being switched-ON. In this transition the benefit of the CMOS
structure is even more evident. In particular, as shown in FIG. 2,
the effect of the drain to source voltage V.sub.DS of the cascoded
switch M1 produces the following effect:
Before the V.sub.DS voltage of M1 (V.sub.S2) reaches the HEMT
threshold voltage, the HEMT is still fully ON, thus the transition
is dominated by the cascoded switch M1;
As soon as the V.sub.DS voltage reaches the HEMT threshold voltage,
the HEMT switch 12, which may be a GaN transistor, starts to
switch-OFF, thereby reducing the current flow.
The output capacitance of the cascoded switch M1 would be charged
by this residual load or even only a leakage current from the
HEMT.
The switch M2 is then switched-ON, allowing for quicker charge of
the Coss of the cascoded switch M1 from the V.sub.CC of the
capacitor C. This effect is similar to adding an already charged
and bigger capacitor (C) in parallel to the output capacitance of
the cascoded switch M1.
This allows a faster establishment of steady voltage on S2, keeping
the HEMT 12 OFF. During OFF time, the capacitor C is charged to the
maximum voltage reached by S2, which is usually higher than the
HEMT threshold.
Although the present invention has been described in relation to
particular embodiments thereof, many other variations and
modifications and other uses will become apparent to those skilled
in the art. It is preferred, therefore, that the present invention
not be limited by the specific disclosure herein.
* * * * *